Cameron Hunter bdf5adc40b Ensure that existing properties are configurable before redefining ...

Summary:
`Libraries/JavaScriptAppEngine/Initialization/InitializeJavaScriptAppEngine.js` attempts to setup global variables typical in most JavaScript environments. It finds the previous property value using `Object.getOwnPropertyDescriptor` and preserves it as `original[PropertyName]` (if it existed), it then redefines the property using `Object.defineProperty`.

Properties may only be redefined if the property descriptor specifies that it is configurable ([MDN](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/getOwnPropertyDescriptor)). Attempting to redefine an non-configurable property will result in an error: `TypeError: Cannot redefine property: [PropertyName]`.

Not all properties being setup in `InitializeJavaScriptAppEngine.js` are necessarily configurable in the target environment.
Closes https://github.com/facebook/react-native/pull/9244

Differential Revision: D3679683

fbshipit-source-id: cd3398ef2cdf38e58c58862e64b159951c2b22c2

2016-08-05 21:58:29 -07:00

..

Initialization

Ensure that existing properties are configurable before redefining

2016-08-05 21:58:29 -07:00

System/JSTimers

Remove exported constants from RCTTimers to allow lazy initialization

2016-07-15 13:58:40 -07:00